DEAR DR. BLONZ: I want your take on the safety of nonstick cooking sprays. What is the propellant used, and how do the sprays work? I use sprays when stir-frying vegetables or roasting a chicken, counting on it to be a healthful practice, as it’s made out to be. But my science-student daughter has advised me that these products may rely on dangerous substances, and that I should switch to straight olive oil. -- L.W., Chicago

DEAR L.W.: Aerosol cooking sprays are based on vegetable oils, such as corn, soy, canola or olive oil. Also in the mix is lecithin, an ingredient from soybeans traditionally used as an emulsifier: a substance that keeps oil and water together in a mix known as an emulsion. Finally, there will either be a pump spray device or a gas propellant.

Such sprays keep food from sticking by forming a thin oil-lecithin film between the cooking surface and the food. Very small amounts of a silicone compound and some alcohol may also be present to prevent foaming and facilitate the formation of the nonstick film. While rubbing a small amount of oil on the pan can also provide nonstick properties, the coating action of cooking sprays tends to be superior, which is especially helpful during cleanup.

Because the sprays use a minimum amount of oil, little fat is contributed to the meal. A one-second application -- an amount sufficient to cover a 10-inch skillet -- will contain less than one gram of fat. Interestingly, the Nutrition Facts labels on many of these spray products have an impractical “recommended serving” of a third of a second or less. This translates to less than a half of a gram of fat per serving, allowing the company to legally label their product as “fat-free.”

The ingredients should be clearly stated, so you can opt for a product that contains no more than the basic components. There’s nothing really unsafe in most sprays, given the small amount used. If there is a safety issue with the ingredients, it would be with aerosol sprays and their compressed-gas propellants. Some use hydrocarbons such as propane or isobutane; both are highly flammable. Such sprays should only be used on cold surfaces and kept away from all flames. There are products that don’t rely on flammable hydrocarbon gas propellants.

Always shake well before using, to thoroughly mix the ingredients. An oft-ignored drawback from the use of these products is the waste contributed by the empty aerosol can. There are refillable pump sprays that limit this waste, but the high pressure of the aerosol is what helps facilitate spray performance. If you go the homemade pump-spray route, you may have to experiment with oils, staying away from unfiltered oils with particulate matter that might clog the nozzle.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: There is an inconsistency I hope you will “weigh in” on. If a pound is the equivalent of 454 grams, and there are nine calories per gram of fat, this would suggest that a pound of body fat will have 4,086 calories. Please explain the common referral to a pound of fat having only 3,500 calories. The math does not add up. -- D.L., East Orange, New Jersey

DEAR D.L.: Fat is our most calorie-dense substance, and it is capable of providing an energy equivalent to nine calories per gram. It is utilized as the primary form of energy storage because humans, like other animals, need to be mobile. If our energy was stored as carbohydrate or protein, the human body would take up over twice the space it does now. Think what size pants you’d need then!

There are 454 grams in a pound, as you correctly point out. So how do we come up with 3,500 calories in a pound, when 454 x 9 = 4,086 calories? The answer rests with the fact that body fat is not pure fat. The adipose tissue that houses the stored fat contains a small amount of water and some structural material, accounting for close to 15 percent of tissue weight. It is this nonfat portion that helps explain why a pound of body fat is said to contain approximately 3,500 calories worth of stored energy.

DEAR DR. BLONZ: I enjoy almonds in many forms, including almond butter, but have been wondering if I get the same nutritional benefits from roasted and unroasted almonds. And what about fat-roasted versus dry-roasted nuts? -- P.W., via email

DEAR P.W.: The roasting of almonds, peanuts or other foods helps to bring about flavor-enhancing chemical reactions in the food. With nuts, this can be accomplished with or without oils, which can impart their own flavor notes. Dry roasting requires specially designed ovens that use heated air to do the cooking. The processor can then add salt, paprika or other flavorings as desired.

Oil roasting adds only about a gram of fat per 1-cup serving. This small difference is explained by the fact that half the weight of the nut -- and more than 70 percent of its calories -- comes from the fats already present. The addition of flavorings, depending on the type used, can affect the level. Honey-roasted nuts, for example, contain less fat per serving because some of the weight is taken up by the sugary coating.

Roasting, being a high-heat process, does destroy some of the heat-sensitive nutrients, which include thiamine and vitamin C. But don’t view this as the deciding factor, as almonds are not the go-to food for these nutrients anyway. Other nutrients are unaffected. Check the complete list of nutrients for almonds at the USDA database: ndb.nal.usda.gov/ndb.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: I have questions about caffeine and alcohol and their effects on hydration. A blog explained that caffeinated beverages are diuretics, and that when you drink 8 ounces of a caffeinated beverage such as tea, coffee or soda, your body will lose 12 ounces of water. That would mean that these beverages are dehydrating instead of hydrating. It made little sense to me, but this was written by people described as experts. Where does alcohol rank as a diuretic? -- M.S., Hayward, California

DEAR M.S.: A word about “experts” on blogs, podcasts or whatever: Have filters in place when you encounter “expert” as a descriptive. Keep the information they offer “on hold” until you are confident of their training and ability to demonstrate an objective, evidence-based foundation for their statements. There are a variety of unaccredited “pay-to-play” organizations selling what appear to be legitimate advanced degrees or proclamations of “board-certified” expertise. Some of these dubious credentials require nothing more than a hefty check, with perhaps a few online courses. Not really what you would assume from one claiming expertise. Some posers are great salespeople -- another red flag being when messages are associated with products being sold.

Diuretics are substances that increase urine output. By this definition, even water could be considered a diuretic. Caffeine is considered to have a mild diuretic effect, but caffeinated beverages such as those you cite would not draw more water out of the body than they contribute. If, however, you were to take caffeine as an over-the-counter or dietary supplement product, it makes sense to be well-hydrated before you start.

The National Academies of Science’s Health and Medicine Division has established a Daily Reference Intake (DRI) for water. The guidelines state that adequate hydration is a daily intake of 2.7 liters (91 ounces) of water for women over the age of 19, and 3.7 liters (125 ounces) for men. Those who are active or live in hot climates may need to consume more. About 80 percent of this total would come from drinking water and other beverages, including caffeinated beverages. The rest comes from food. Vegetables and fruits, for example, are mostly water by weight.

Alcohol also has a mild diuretic effect, but it works differently. One of its effects is to inhibit the release of anti-diuretic hormone (ADH), a hormone that limits the amount of urine produced in the body. When alcohol is around, less ADH is released, which translates to more urine leaving the body. The effects are present in about 20 minutes, which any beer drinker is likely to affirm.

Alcohol’s diuretic effects play an interesting role, and many of alcohol’s effects depend on the blood concentration of its metabolites. The body has a rate at which it processes alcohol, and it uses its fluids as a storage queue for metabolic byproducts awaiting processing and elimination. As such, alcohol’s diuretic effect enhances the consequences of over-consumption.

Tolerance to alcohol is said to be weight-related: The larger you are, the more you can tolerate. This is not so much because larger individuals metabolize alcohol faster, but because a larger body has a greater blood volume to begin with.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.